<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <script>
        //第二次作业
        let pi = 3.14,r = prompt('请输入半径cm：'),s =pi*r**2
        document.write(s)
    </script>
</body>
</html>